The present disclosure relates generally to light emitting diode (LED) assemblies and their applications, more specifically to the LED assemblies suitable for omnidirectional light appliances.
LED has been used in different kinds of appliances in our life, such as traffic lights, car headlights, street lamps, computer indicators, flash lights, LCD backlight modules, and so on. LED chips, which are used as light sources for appliances, are produced by wafer manufacturing process in the front end, and then undergo LED packaging in the back end to result in LED assemblies or apparatuses.
LED packaging mainly provides mechanical, electrical, thermal and optical supports to LED chips. LED chips, which are kind of semiconductor products, are prone to degradation, or aging, if being exposed for a long time in an atmosphere full of humidity or chemical. To isolate the LED chips from unfriendly atmosphere, epoxy resins are commonly used to cover and seal them. Heat dissipation and light extraction should be also considered for LED packaging, such that LED products could have long lifespan and high brightness. For example, the heat generated at a p-n junction in an LED chip, if not being well dissipated, could deteriorate the LED chip, shorten its lifespan, and downgrade its reliability. Optical design, such as the way to extract and direct the light into a desired angle or distribution, also plays an important issue for LED packaging.
Design for packaging white LEDs is more complex and needs to further consider color temperature, color rendering index, phosphor, etc. A white LED could be provided using phosphor to convert a portion of the blue light from a blue LED chip into green/yellow light, such that the mixture of the lights is perceived as white light by human eyes. Because human eyes are vulnerable to high-intensity blue light, the blue light from a blue LED chip in a white LED package should not emit outward directly without its intensity being attenuated. In other words, the blue light should be kind of “sealed” or “capsulated” so as to prevent blue light leakage to human eyes.
Furthermore, it is a constant trend in the LED industry to pursue LED packaging processes with high stability, low cost, and high product yield.